The helmet of a road-going cyclist or motorcyclist is a very important safety component, in that it shields the user's head from impact injury. Such head impact injury is usually a consequence of lateral tilting (falling) to the ground of the bicycle or motorcycle in motion. Indeed, as is well known by those familiar with such vehicles, the lateral stability thereof is dynamically enabled--i.e., it is because the vehicle is in forward motion that it can remain upright without falling laterally to the ground. See for example U.S. Pat. No. 5,231,703 issued Aug. 3, 1993 to the present inventor.
It has also been discovered in the field that, for (non-powered, i.e. person-pedalling) bicycles at least, the contour or shape of the helmet does have an influence on the performance of the vehicle, particularly with respect to the top speed that can be achieved with the vehicle, the lateral wind sensitivity values, and generally speaking the power output that can be efficiently delivered. This is because, as bicycle speed increases, helmet-induced aerodynamic drag also increases.
A quick review of basic notions of aerodynamics would not be irrelevant. Aerodynamics is the branch of dynamics that treats of the motion of air and other gaseous fluids and of the forces acting on solids in motion relative to such fluids. When an airfoil is moved at subsonic speeds through the air, the motion produces a pressure at every point of the airfoil which acts orthogonally to the surface. In addition, a frictional force tangential to the surface opposes the motion. The sum of these pressure and frictional forces gives the resultant force acting on the airfoil.
Drag D, or resistance on an airfoil wing, can be defined by the following formula: EQU D=C.sub.D 1/2.rho.V.sup.2 S
where:
C.sub.D is the wing chord; PA1 .rho. is the density or air; PA1 V is the apparent air velocity; and PA1 S is the wing area.
Therefore, it can be readily understood that drag is a function of the square of the relative wind velocity V, as well as a function of the wing area. Thus, a small increase in (head) wind speed translates into a much greater increase of the wind-induced resistance to motion.
With these teachings in mind, bicycle helmet designers have developed the current state of the art bicycle helmets in such a way as to streamline same to approximate the contour of an airfoil. Hence, airfoil aerodynamic designs have been extended to apply to bicycle helmets. Therefore, it can now be understood that a small incremental increase in head wind for the cyclist will translate into a correspondingly much greater incremental increase in drag, which is to say, a much greater pedalling effort will be required from the cyclist for a given speed and a much lower top speed value would normally be achieved for a given power output. Since the power output of a cyclist is usually quite small--about 1/4 to 1/2 horsepower (approximately 180 to 360 Watts) at peak output--head wind speed will have a considerable effect on the speed of the bicycle.
It is to be remembered also that, for the so-called high-speed bicycles with the handsets being offset at a point of the bicycle much ahead and quite low, the cyclist must take a position whereby the head becomes the frontmost part of his body. That is, the cyclist head becomes the leading edge of the cyclist body, much like the leading edge of an airfoil wing. Hence, the contour of this leading edge helmet becomes a significant component in the performance-enhancing equipment of cyclist's gear.
Empirical on-the-field studies have shown time and again that such helmet streamlining does provide significant performance enhancement of bicycle performance.
Clearly therefore, any bulk part projecting orthogonally from the helmet would considerably affect the aerodynamic drag thereof, by inducing turbulence which would significantly increase the drag. Indeed, such bulk part would increase the "wing chord" and/or the "wing area" of the helmet, and would therefore increase drag D in the above-noted formula as parameters C and S.
A third feature of helmets have been their modifications to act as a template for receiving and supporting a visual warning device for alerting motorists of the presence of the cyclist on the road during non-daylight periods. U.S. Pat. No. 4,186,429 issued Jan. 29, 1980 to Walter JOHNSTON discloses such a helmet 12 being provided with a light 30 secured by its plastic base 16 to the top portion of the helmet by a rubber cup 14. As clearly seen in FIG. 1, this light and base assembly 30, 16, projects orthogonally from the helmet; and the helmet is not of the streamlined, airfoil type, but rather, of an old-design, dome type. There is also envisioned that the light be powered autonomously by a battery pack carried on the cycle or by the cyclist.
More recent U.S. Pat. No. 4,901,210 issued Feb. 13, 1990 to Akira HANABUSA, discloses a dome-shaped motorcycle helmet with a warning light carried at the aft end of the helmet. In one embodiment--FIG. 11--, hook and loop fasteners (sold under the registered trademark VELCRO) are envisioned to be used as securing means for securing the light support member to the helmet frame. In another embodiment--FIG. 15--, holes are made through the helmet to receive bolts, said bolts to secure the light to the helmet. This light is claimed to be entirely self-contained, carrying its own power source; as well as to be detachable from the helmet in the event of an accident, to prevent it from snagging the helmet and causing injury to the wearer.
U.S. Pat. No. 2,788,439 issued in 1957 to Gilbert HESSE (from St-Calixte, Quebec) is another example of such light warning device, but here for use over a soft fabric, hunter-type hat (as per the safety pin 2 that is to pierce the hat).
A fourth consideration in bicycle helmet construction is the aesthetic design thereof. More and more, helmets do tend to convey a sense of visual appeal that promotes their sale and their use, as their above-noted functional features, although paramount, do not exclude aesthetic qualities. Clearly, a bicycle helmet which has a non-aesthetic appearance will not sell well, or else, if purchased, may not be worn. Indeed, those persons most likely to benefit from such helmets, namely children and teenagers, will likely be induced not to wear them if they feel in any way that they will look silly, due to the strong peer pressure at that age "not to look like a nerd". Hence, for such reasons, owning an helmet but not wearing it is no doubt a greater safety hazard, because it can bring a false sense of security. This is where the design and the utility parts of the patent protection effectively merge together.